1. Field of the Invention
The present invention relates generally to IEEE 802.16 wireless metropolitan networks (WMAN) and the wireless stations (e.g., subscriber station (SS), mobile station (MS), or relay station (RS)) of such a network. More particularly, the present invention relates to uplink multiple-input-multiple-output (MIMO) transmissions or cooperative MIMO transmissions for wireless stations each with more than two transmission antennae.
2. Discussion of the Related Art
MIMO and cooperative MIMO techniques enhance system performance in a wireless communication system (e.g., a cellular network or an IEEE 802.16 network) by exploiting spatial domain freedom and signal processing techniques. MIMO and Cooperative MIMO techniques are described, for example, in the article “From theory to practice: an overview of MIMO space-time coded wireless systems,” by D. Gesbert, M. Shafi, and D. S. Shiu, IEEE J. Select. Areas Commun., vol. 21, no. 3, pp. 281-302, April 2003.
Certain wireless network standards (e.g., IEEE 802.16-20041 and IEEE 802.16e2) have adopted MIMO and cooperative MIMO techniques to enhance system performance. Other emerging wireless network standards (e.g., IEEE 802.16j3 and IEEE 802.16m4) are also considering including MIMO and cooperative MIMO techniques to improve system performance (e.g., high data rate or low BER (bit-error-rate)). 1 IEEE Standard for Local and Metropolitan area networks, Part 16: Air Interference for Fixed Broadband Wireless Access Systems. (October 2004)2 IEEE Standard for Local and metropolitan area networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1. (February 2006)3 P802.16j PAR, P802.16j-Amendment to IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems—Multihop Relay Specification. (March 2006; see, e. http://standards.ieee.org/board/nes/projects/802-16j.pdf)4 P802.16m P802.16—IEEE Standard for Local and metropolitan area networks—Part 16: Air Interface for Fixed Broadband Wireless Access Systems—Amendment: IEEE Standard for Local and metropolitan area networks—Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems—Advanced Air Interface (see, e.g., http://standards.ieee.org/board/nes/projects/802-16m.pdf) (December 2006)
MIMO techniques are classified into many types, including 1) Spatial multiplexing; 2) Space-time-frequency coding (STFC); 3) Precoding; and 4) Others (e.g., antenna selection and antenna grouping). In a MIMO transmission scheme, a MIMO coding matrix is defined which specifies the signals to be transmitted by different antennae at different times and frequency resource. The Cooperative MIMO technique is a variation of the MIMO techniques. In a cooperative MIMO technique, multiple wireless stations act as different antennae of a conventional MIMO transmitter to form an antenna array which transmits data simultaneously to a BS. The cooperative MIMO technique provides higher uplink spectrum efficiency.
The effectiveness of a MIMO technique is related to the number of transmission antennae. For example, in STFC under a given standard, the MIMO coding matrices are defined for different number of transmission antennae, so that a wireless station having only two transmission antennae cannot use STFC matrices defined for a wireless station with three or four antennae under that standard. Under different standards, the number of allowed antennae is different. For example, under the IEEE 802.16-2004 and the IEEE 802.16e standards, the number of supported transmission antennae of a wireless station is one or two. FIG. 1 shows an exemplary uplink transmission under the IEEE 802.16-2004 standard or the IEEE 802.16e network standard. Under the IEEE 802.16-2004 and IEEE 802.16e standards, uplink transmission is carried out using the following steps:                (a) a wireless station (WS) negotiates with a base station (BS) regarding the uplink MIMO/cooperative MIMO capabilities that may be used in its transmissions;        (b) the WS sends a request to the BS for uplink transmission when the WS has data to be transmitted;        (c) the BS determines the uplink MIMO/cooperative MIMO method (e.g., stream number, STFC matrix, antenna grouping method, and precoding matrix) to be used by the WS, according to the BS's measurement of its channel, the bandwidth requests of the wireless stations, and other parameters;        (d) through an “Information Element” (IE), the BS informs the WS of the resource allocated to the uplink transmission and the MIMO/cooperative MIMO method for the uplink transmission to be used by the WS;        (e) the WS maps data symbols and pilot symbols to the allocated resource, according to pre-defined data mapping rules and pilot patterns indicated in the IE, and performs the MIMO/cooperative MIMO transmissions using the allocated resource; and        (f) the BS performs channel estimation and signal detection to detect the received data.        
In general, negotiation for the uplink MIMO/cooperative MIMO can be performed when the WS enters the network. The MIMO/cooperative MIMO capabilities refer to such capabilities as supported STFC matrices, antenna selection ability, antenna grouping ability, precoding ability, vertical coding ability, or horizontal coding ability. Under the IEEE 802.16-2004 and the IEEE 802.16e standards, subscriber station basic capability request (“SBC-REQ”) and subscriber station basic capability response (“SBC-RSP”) messages are used by a WS and a BS to negotiate the uplink MIMO/cooperative MIMO capabilities.
FIG. 2 shows the conventional type length value (TLV) field of SBC-REQ and SBC-RSP messages under the IEEE 802.16-2004 and IEEE 802.16e standards. FIG. 2 shows that the supported uplink MIMO/cooperative MIMO capabilities are: 1) space time transmit diversity (STTD) using two antennae, 2) spatial multiplexing (SM) with vertical coding using two antennae, and 3) single antenna cooperative SM. Therefore, the SBC-REQ and SBC-RSP messages under IEEE 802.16-2004 and IEEE 802.16e standards do not support a WS having more than two antennae.
Examples of IEs used between a BS and a WS under the IEEE 802.16-2004 and IEEE 802.16e standards for communicating the resource allocation and uplink MIMO/cooperative MIMO method include MIMO uplink basic IE (“MIMO_UL_Basic_IE”) and MIMO uplink enhanced IE (“MIMO_UL_Enhanced_IE”). Since MIMO_UL_Enhanced_IE encompasses more functions than MIMO_UL_Basic_IE, the following detailed description uses MIMO_UL_Enhanced_IE to illustrate the present invention. FIG. 3 shows the format for a MIMO_UL_Enhanced_IE. As shown in FIG. 3, the Matrix_Indicator (MI) field specifies the MIMO method to be used for uplink transmission. For a WS station with dual antennae, the MI field specifies an STTD matrix. For a WS with a single antenna, the MI field is ignored. The Pilot Pattern Indicator (PI) field specifies a pilot pattern to be used by a WS in an uplink transmission. Thus, as is apparent from FIG. 3, the MIMO_UL_Enhanced_IE supports only MIMO/cooperative MIMO methods for WS's with two or less antennae. New methods should be developed for resource allocation and MIMO/cooperative MIMO methods that support a WS with more than two antennae.
In step (e) discussed above, a WS uses the MIMO coding matrix specified in the IE to perform MIMO encoding, and to map the coded data symbols to the allocated resource with a proper pilot pattern. The uplink basic resource unit is named a “tile,” one example of which is shown in FIG. 4. As shown in FIG. 4, a tile includes 12 subcarriers, four of which encode pilot symbols (i.e., the other eight subcarriers used for encoding data symbols). The tile is over three OFDMA symbols in the time domain and over four subcarries in the frequency domain. For uplink transmissions, a WS maps the coded data symbols to the tile. FIGS. 5 and 6 show the data mapping rules for 2-antenna STTD under the IEEE 802.16-2004 standard and the IEEE 802.16e standard, respectively. As shown in FIGS. 5 and 6, the frequency axis has a higher priority than time axis, (i.e. the coded data symbol first maps to the subcarriers within the tile and then to different OFDM symbols within the tile).
The pilot patterns used by a WS in the IEEE 802.16-2004 standard and the IEEE 802.16e standard are determined according to:                (I) For a WS with one antenna, either pilot pattern A or pilot pattern B of FIG. 5 is adopted; the BS determines the pilot pattern to be used by the WS; and        (II) For a WS with two antennae, either: (i) antenna 1 uses pilot pattern A and antenna 2 uses pilot pattern B (pilot patterns A and B are shown in FIG. 5); or, (ii) antenna 1 uses pilot pattern C and antenna 2 uses pilot pattern D (pilot patterns C and D are shown in FIG. 6); the BS determines the pilot patterns to be used by the WS.        
Therefore, the data mapping rules and pilot mapping rules under the IEEE 802.16-2004 and the IEEE 802.16e standards support data and pilot mapping rules for MIMO/cooperative MIMO methods for one or two antennae. No data mapping and pilot mapping rules are provided to support a WS with more than two antennae.
In step (e) above, the BS performs channel estimation and proper signal detection according the uplink MIMO/cooperative MIMO method to detect the signals of WS's in the allocated resource.
As is apparent from the above detailed descriptions of the uplink MIMO/cooperative MIMO transmission procedures in the IEEE 802.16-2004 and the IEEE 802.16e standards, the IEEE 802.16-2004 and IEEE 802.16e standards cannot support uplink MIMO/cooperative MIMO transmissions for a WS with more than two antennae. However, with the rapid development of the MIMO techniques, WS's with three or four antennae have become common place. For example, a relay station (RS) in an IEEE 802.16j network typically has three or four antennae (see, e.g., IEEE 802.16j-06/015, “Harmonized Contribution on 802.16j (Mobile Multihop Relay) Usage Models”). Under the IEEE 802.16m standard, a mobile station (MS) may also have three or four antennae. Thus, on one hand, current IEEE 802.16-2004 and IEEE 802.16e standards do not support WS's with three or four antennae, and no implementation is known for uplink MIMO/cooperative MIMO transmissions for a WS with three or four antennae. On the other hand, such an implementation is required by the IEEE 802.16j and IEEE 802.16m standards, for example.
Thus, the following methods are needed to implement uplink MIMO/cooperative MIMO transmissions for a wireless station with three or four antennas.                (a) methods for a WS with three or four antennae to negotiate MIMO/cooperative MIMO capabilities with a BS;        (b) concrete MIMO/cooperative MIMO methods for uplink transmissions of a WS with three or four antennae;        (c) methods for informing a WS of the uplink MIMO/cooperative MIMO methods to be used and the allocated resource; and        (d) a pilot pattern to be used by a WS with different transmission antenna, and data mapping rules to map data symbols after MIMO encoding to the tile.        